Cryogenic pump system

ABSTRACT

A cryogenic pump system having low heat leak and low net positive suction head. The supply and vent lines between a pump and a cryogenic liquid storage Dewar are contained in a vacuum jacket manifold which provides vacuum insulation over the entire length of the lines. The manifold has bellows sections for flexibility and is adapted for bayonet connection to the storage Dewar outlets. The pumping element or &#39;&#39;&#39;&#39;cold end&#39;&#39;&#39;&#39; of the pump is insulated by a horizontal Dewar which also encloses a relatively small sump flooding only the suction port of the pump. The sump is filled with cryogenic liquid via the supply line, appropriate liquid level being maintained by a vent dip tube connected to the storage Dewar vent line. A Venturi built into the vent dip tube and powered by the piston ring blowby aspirates excess liquid from the sump.

ilnited States Patent Primary Examiner-William L. Freeh Attorney-Hinderstein & Silber ABSTRACT: A cryogenic pump system having low heat leak and low net positive suction head. The supply and vent lines between a pump and a cryogenic liquid storage Dewar are contained in a vacuum jacket manifold which provides vacuum insulation over the entire length of the lines. The manifold has bellows sections for flexibility and is adapted for bayonet connection to the storage Dewar outlets. The pumping element or cold end of the pump is insulated by a horizontal Dewar which also encloses a relatively small sump flooding only the suction port of the pump. The sump is filled with cryogenic liquid via the supply line, appropriate liquid level being maintained by a vent dip tube connected to the storage Dewar vent line. A Venturi built into the vent dip tube and powered by the piston ring blowby aspirates excess liquid from the sump.

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CARL A. GRENCI ATTORNEYS PATENTEUJAN 4m SHEET 2 BF 3 m oI INVENTOR.

CARL A. GRENCI ATTORNEYS CRYOGENIC PUMP SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic pump system, and more particularly to such a system wherein the lines interconnecting a pump and a cryogenic liquid storage Dewar are contained in a vacuum jacket manifold. The invention also relates to a vacuum insulated cryogenic pump utilizing a novel sump arrangement for flooding only the input part of the pump.

2. Description of the Prior Art Compressed gas cylinders typically are filled by pumping oxygen, hydrogen, nitrogen or the like from storage Dewars containing the gas in liquid form at cryogenic temperatures. For most efficient operation of such cylinder recharging systems, the oxygen, etc. should be maintained in the liquid state while being pumped, a vaporizer then being used to convert the pump discharge to the gas phase.

To prevent saturation of cryogenic liquid in such recharging systems, it is desirable to vacuum insulate the supply and vent lines between storage Dewar and pump, as well as to minimize heat leakage to the cold end" or pumping element of the pump.

In the past, complex mechanical arrangements have been used to accomplish insulation of the pumpstorage Dewar interconnections. For example, one approach of the prior art has been to mount the pumping element directly into the storage Dewar. Another approach, typified by US. Pat. No. 3,260,061 to R. S. Hampton et al., is to provide a conduit protruding from the storage Dewar outer vacuum jacket. The conduit, which extends all the way to the pump, contains the supply and vent lines, the conduit interior forming an extension of the storage Dewar vacuum space.

Such prior art approaches suffer the disadvantage of requiring substantial modification of the storage Dewar itself. Moreover, they are not practical for inthefield operation, since the prior art storage Dewar. In addition, such systems are difficult to service and repair.

The problem of limiting heat leak to the cold end of a cryogenic pump also has been considered in the past. Typically, the entire pumping element has been immersed into the cryogenic liquid, either by mounting the pump directly into the storage Dewar, or by providing a separate flooded sump surrounding the entire cold end. This latter approach is illustrated by U.S. Pat. No. 3,083,648 to L. E. Putnam, wherein a vacuum insulated sump, completely filled with cryogenic liquid, floods both the input (suction) and output (discharge) parts of the pump.

While such prior art flooded sump techniques provided relatively low net positive suction head (NPSH), they had the serious shortcoming of having the cryogenic supply liquid in direct contact with the pump cylinder and discharge line. Since the pump discharge tends to be at a higher temperature than the supply liquid, this in itself causes undesirable heat leak into the cryogenic liquid. Moreover, since inadequate means were provided to maintain a pressure differential between the suction (supply) and vent lines, circulation of cryogenic liquid through the system was limited, giving rise to a long stay time. That is, the average time which cryogenic liquid remained in the sump before actually being pumped was considerable, thus increasing the likelihood of evaporation.

The present invention overcomes these and other shortcomings of the prior art by providing a novel cryogenic pump system wherein the lines between pump and storage Dewar are vacuum insulated, yet can be connected and disconnected tion of cryogenic liquid through the system, thereby insuring low stay time in the sump.

SUMMARY OF THE INVENTION The present invention comprises a cryogenic pump system useful for recharging compressed gas cylinders from a source of cryogenic liquid stored in a Dewar. The system includes a storage- Dewartopump interconnection apparatus wherein supply and vent lines are vacuum insulated in a flexible vacuum jacket manifold, and further includes a vacuum insulated pump providing flooded suction to the input port, yet maintaining insulation between the supplied cryogenic liquid and both the discharge line and environmental ambient.

The supply and vent lines are contained within the vacuum jacket manifold having a common portion through which lines extend, and which is adapted for connection to a cryogenic pump. The manifold also includes first and second tubular projections through which extend the supply and vent lines respectively. These tubular projections each include a bellows section for flexibility. The ends of the projections are of reduced diameter to permit bayonet insertion thereof into the supply and vent outlets of the storage Dewar. The supply and vent lines are spaced from each other and from the interior wall of the jacket manifold, and the manifold interior is evacuated, thereby providing vacuum insulation of the Dewartopump interconnection lines for their length.

The vacuum insulated pump comprises a horizontal Dewar which fits over the cold end or pumping element of a generally conventional cryogenic pump. A relatively small sump is contained within the horizontal Dewar enclosure, the suction or input port of the pump extending into the pump. The discharge port of the pump, while contained within the Dewar enclosure, is spaced from the sump.

The vacuum jacket manifold is provided with two extensions from its common portion, which extensions project through a wall of the pump Dewar enclosure, providing vacuum insulation of the supply and vent lines directly into the pump enclosure. The supply line extends into the sump, terreadily for inthe-field operation. No major modification of the storage Dewar is required. Further, the invention utilizes a vacuum insulated pump having low net positive suction and incorporating a sump which floods only the inlet port. The discharge line is spaced from the suction liquid to minimize heat leakage thereto. Means are provided to maintain circulaminating at a level below the pump input port. Cryogenic liquid from the storage Dewar is thereby fed via the supply line into the suction sump.

The vent line terminates in a vent dip tube extending into the sump to a level above the pump input port. Built into the vent dip tube is a Venturi powered by the piston ring blowby. The suction created by this Venturi aspirates excess liquid out of the suction sump. The resultant stream of twophase fluid in the vent line return to the storage Dewar helps maintain adequate pressure differential between supply and vent lines to assist circulation of cryogenic liquid through the system.

Thus, it is an object of the invention to provide an improved cryogenic pump system.

Another object of the invention is to provide a cryogenic pump system, for use with a cylinder recharging system or the like, wherein the storage- Dewartopump interconnection lines are vacuum insulated for their entire length, yet requiring no substantial modification of the storage Dewar itself.

It is another object of the invention to provide an apparatus for interconnecting a cryogenic pump and a storage Dewar containing a cryogenic liquid, the apparatus including supply and vent lines vacuum insulated within a partially flexible manifold.

Still another object of the present invention is to provide a vacuum jacket manifold apparatus for insulating Dewar supply and vent lines, the manifold including projections, containing vacuum insulated lines therewithin, adapted for bayonet insertion into the Dewar supply and vent outlets.

It is still another object of the present invention to provide an improved vacuum insulated cryogenic pump.

A further object of the present invention is to provide a vacuum insulated pump having low net positive suction head, and including a sump providing flooded suction to the pump input port, yet isolated from the pump discharge line.

It is a further object of the present invention to provide a vacuum insulated cryogenic pump including a suction sump wherein the cryogenic liquid is circulated by a Venturi powered vent dip tube communicating with the storage Dewar vent line.

Still a further object of the present invention is to provide a cryogenic pump having its cold end" vacuum insulated by a Dewar enclosure, and including a relatively small suction sump within the enclosure, the sump providing flooded suction only to the pump input port, cryogenic liquid circulation in the sump being maintained by a Venturi system powered by the pump piston ring blowby.

BRIEF DESCRIPTION OF THE DRAWINGS Still other objects, features and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of the preferred embodiments constructed in accordance therewith, taken in conjunction with the accompanying drawings wherein like numerals designate like parts in the several figures and wherein:

FIG. 1 is a perspective view, partly broken away in section and partly diagrammatic, of a cryogenic pump system in accordance with the present invention;

FIG. 2 is a sectional view of the inventive low heat leak, low net positive suction head, vacuum insulated cryogenic pump as seen generally along the line 22 of FIG. 1;

FIG. 3 is a sectional view of the low heat leak, low net positive suction head, vacuum insulated cryogenic pump as seen generally along the line 33 of FIG. 1; details of the vent dip tube including a ring blowby powered Venturi are evident in this view.

FIG. 4 is a sectional view along the line 44 of FIG. 1, showing the separation between the supply and vent lines within the vacuum jacket manifold.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and particularly to FIG. 1 thereof, there is shown a cryogenic pump system in accordance with the present invention. The system utilizes vacuum jacketed storage- Dewartopump interconnection lines and employs a unique vacuum insulated pump having low heat leak and low net positive suction head. As illustrated in FIG. 1, the inventive vacuum insulated pump 6, in conjunction with a conventional vaporizer 8, may be employed for recharging a compressed gas cylinder 10, a with oxygen, hydrogen, nitrogen, argon or the like, the gas being supplied from a storage Dewar 12 containing the material in liquid form at cryogenic temperatures.

Supply Dewar 12 is of conventional construction, and includes an inner wall 14 and outer wall 16 separated by a vacuum space 18. A supply 20 of liquid oxygen, hydrogen, nitrogen, argon or the like, is maintained within Dewar 12. For oxygen, the temperature of liquid 20 is on the order of -297 F. or higher. The vapor space 22 within Dewar 12, above liquid 20, typically has a pressure of from zero to 200 pounds per square inch. Although not illustrated, storage Dewar l2 normally is provided with a vent release line leading from vapor space 22 to a conventional relief valve,

As shown in FIG. 1, a vent tube 24 has an open end 26 extending into the upper portion of vapor space 22. Vent tube 24 extends within vacuum section 18, terminating at an outlet 28 adjacent the lower end of Dewar 12. To facilitate utilization of the inventive system of vacuum jacketed lines, a flange 30 has been provided about the lower end of vent outlet 28. Cryogenic liquid 20 is supplied from Dewar 12 via a supply outlet 32 situated at the center of the convex lower end of storage Dewar 12. Supply outlet 32 is surrounded by portion 18a of vacuum space 18, and terminates in a neck region 32' about which is situated a flange 34.

lnterconnections between storage Dewar 12 and vacuum insulated pump 6 are facilitated by a novel system of vacuum jacketed lines contained within a manifold indicated generally at 36 in FIG. 1. The system includes a supply line 38 and a vent line 40, both of which are contained within vacuum jacket manifold 36. Manifold 36 preferably is of stainless steel or the like, and includes a common tubular portion 42 adapted for attachment (in a manner described below) to pump 6, a first tubular projection 420 having a neckeddown end region 42b, and a second tubular projection 42c having a neckeddown end region 420. As indicated in FIGS. 1 and 4, a plurality of spacers 44 insure that lines 38 and 40 are maintained in spaced relationship from each other and from the interior wall of vacuum jacket manifold portion 42. The region 46 within manifold 36 forms an enclosed vacuum space.

Vent line 40 includes a generally vertical section 40a contained within vacuum jacket manifold projection 42a. Vent tube 40 terminates at an end 40b which is surrounded by manifold end region 42b, which region has an outer diameter smaller than that of manifold portion 42a. The outer diameter of manifold end region 42b is slightly smaller than the inner diameter of vent outlet 28, so as to permit sliding or bayonet insertion of manifold end 42b within outlet 28. Since the outer diameter of vent line section 40a is smaller than the inner diameter of manifold end region 42b, a vacuum space insulates vent line section 40a all the way to end 40b, this vacuum insulation extending within channel 28.

An annular flange 48 surrounds the lower portion of vacuum jacket manifold end region 42b. Flange 48 seats against flange 30 when end region 42b is inserted within vent outlet 28, as illustrated in FIG. 1. Although not shown, flanges 30 and 48 may be connected together by appropriate bolts or the like.

To prevent leakage of fluid between the interior of vent outlet 28 and the exterior of end region 42b of vacuum jacketed manifold 36, a springloaded Teflon seal 50 is provided in an appropriate groove about the periphery of end region 42b. In addition, a Teflon/asbestos gasket 52 is provided between flanges 30 and 48.

A conventional vacuum jacketed valve 54 is provided as an integral part of vent line 40a and vacuum jacket manifold projection 420. In addition, to provide some flexibility for positioning manifold end region 42b within outlet 28, vent line section 40a and manifold projection 42a are provided with bellows 56 and 58, respectively. The space 60 between bellows S6 and 58 communicates with region 46 within manifold 36, and so forms a portion of the vacuum space insulating vent line 40. A pair of flanges 62 and 62' are provided at the interface between bellows 58 and manifold sections 42 and 420. A rigid metal spacer 64 extends between flanges 62 and 62', surrounding bellows 58. When spacer 60 is evacuated, bellows 56 and 58 tend to contract, pulling flanges 62 and 62' toward one another; rigid spacer 64 limits this travel, thereby preventing collapse of bellows 56 and 58.

Still referring to FIG. I, a generally vertical section 38a of supply line 39 terminates at an upper end 38b. Section 380 extends within vacuum jacket manifold tubular projection 42c and within neckeddown end region 42d. The outer diameter of vacuum jacket end region 42d is slightly smaller than the inner diameter of supply outlet 32 of storage Dewar 12. This permits sliding or bayonet insertion of end region 42d into outlet 32, the extent of insertion being limited by an annular flange 66 provided around manifold end region 42d. Flange 66 may be connected to flange 34 by bolts or the like (not shown), when manifold 36 is connected to Dewar 12 as shown in FIG. 1. Leakage of cryogenic liquid 20 between the outer wall of vacuum jacket manifold end region 42d and the inner wall of outlet 32 is prevented by means of a springloaded Teflon seal 68 peripherally mounted in the exterior wall of manifold end region 42d. Also, a Teflon/asbestos gasket 70 may be provided between flanges 66 and 34.

Fluid flowing through supply line section 38a is controlled by a conventional vacuum insulated valve 72. Further, supply line section 38a includes a bellows section 74, surrounded by a bellows section 76 which connects vacuum jacket manifold sections 42 and 420. The space 78 between bellows sections 74 and 76 communicates with manifold interior region 46 so as to form part of the vacuum region insulating supply line 38. A pair of flanges 80 and 80' are provided at the interfaces between bellows 76 and vacuum jacket manifold sections 42 and 420. A metal spacer 82, surrounding bellows section 76, limits the travel of flanges 80 and 80' toward one another when region 78 is evacuated.

Still referring to FIG. 1, pump 6 is of the positive displacement type, horizontally configured, and includes a conventional crank case 84 and crosshead 86, and is supported by mounting brackets 88. Pump 6 is driven from a motor, not shown, via a shaft 90. Rotation of shaft causes reciprocation of a piston 92 (see FIGS. 2 and 3) within the cold end or pumping element 94 of pump 6. As will be discussed in detail hereinbelow, cold end 94 is situated within a horizontal Dewar enclosure 96, which enclosure also houses a suction sump 98 which holds cryogenic liquid supplied via line 38.

Liquid discharge by pump 6 is fed via a discharge line 98 to vaporizer 8. Vaporizer 8, which may be electrically heated, vaporizes the pump discharge fluid to provide gas under pressure via lines 100, 100a to fill cylinders 10, 10a. Dewar enclosure 96 is provided with a low-pressure bleed line 102 which leads via a control valve 104 and a relief valve 106 to environmental ambient.

Details of the inventive vacuum insulated pump 6 are evident in FIGS. 2 and 3. Referring thereto, it may be seen that the cold end 94 of pump 6 extends through a back flange 108 of Dewar enclosure 96. Specifically, back flange 108 is provided with an opening 110 permitting insertion therethrough of cold end 94. The rear, threaded end 112 of pumping element 94 extends rearward of opening 110, threadingly engaging the forward end of pump housing 114. (Housing 114, also evident in FIG. 1, itself extends between pumping element 94 and a flange 116 at the forward end of a crosshead 86.) Back flange 108 is maintained in place by an interiorly threaded locking ring 118 engaging a threaded portion 120 of pumping element 94. A spring energized Teflon seal 122 seats within opening 110 between ring nut 118 and the forward end of housing 1 14 of prevent fluid leakage.

Except for some minor modifications noted below, cold end" or pumping element 94 is conventional, and includes a generally cylindrical chamber 124 within which piston 92 reciprocates. Piston 92 itself is provided with conventional piston rings 126 and a guard ring 128. Situated within the forward end of pumping element 94 is a suction or inlet port 130 comprising a suction valve 132 which reciprocates in an inlet valve guide 134. Valve 132 is biased against a valve seat 136 by means of a coil spring 138 surrounding the stem of valve 132 within a recess in guide 134. Spring 138 presses against a nut 132a attached to valve 132.

A pump discharge port 140 is situated on a vertically extending portion 142 of pumping element 94. A discharge guide 144 extends into a recess 146 in portion 142, being maintained therein by a discharge nut 148. Nut 148 itself threadingly engages the upper end of recess 146. Situated within charge guide 144 is a discharge valve or poppet 150 which is biased against a seat 152 by a coil spring 154.

conventionally, a poppet 150 comprises a stainless steel ball. However, it has been found that such a stainless steel poppet tends to work harden from impact against seat 152 when pumping liquids at cryogenic temperatures. This work hardening prevents the poppet from completely closing against seat 152, resulting in leakage at this interface. By utilizing a discharge poppet 150 fabricated of reinforced Teflon, this leakage problem has been completely eliminated.

Surrounding piston 92 (see FIG. 3) rearward of piston rings 126 in an enlarged cylindrical recess 156 within pumping element 94. Situated in the forward end of recess 156 is a steel spacer 158 against which is positioned a stainless steel ring 160 having a slightly tapered cross section. Ring 160 is slotted to provide communication between chamber 124 and a ring blowby port 162, the function of which will be described below. Situated behind ring 160, within recess 156, are a plurality of Bellville springs 164. Springs 164 function to bias a packing, comprising a plurality of tapered stainless steel rings 166 each associated with a glass-filled Teflon packing 168, against a packing gland 170. Packing gland 170 itself is rigidly attached to the rear end of pumping element 94 by means of bolts 172. A scraper ring 171 is provided in packing gland 170 to scrape piston 92 as the piston reciprocates.

In accordance with the present invention, pump inlet or suction port 130 is flooded with cryogenic liquid contained in suction sump 98. Referring to FIGS. 2 and 3, sump 98 is generally cuplike in shape and preferably is fabricated or stainless steel or other material which will not become brittle at cryogenic temperatures. Sump 98 includes an open top 980, a closed bottom 98b and sides 98c, 98d. A circular opening is provided in side 98d, through which projects pump inlet port 130. Sump 98 is supported by means of a spacer 174 and a ring nut 176 which threadingly engages the threaded exterior of pumping element 94. Sump 98 is filled with cryogenic liquid via supply line 38, as described below.

Referring to FIGS. 1, 2 and 3, manifold 36 is provided with a manifold extension 178, generally at a right angle to manifold common portion 42, and extending through back flange 108. Manifold extension 178 surrounds a supply line section 38c which communicates with line 38, and which extends into the interior of horizontal Dewar enclosure 96 via manifold end 178'. The interior region 180 between supply line section 38c and manifold extension 178 communicates with vacuum region 46 so as to form a portion of the vacuum space insulating supply line 38.

As best shown in FIGS. 2 and 3, line 380 is connected via an appropriate coupling 182 with a supply tube 184. Supply tube 184 is curved to form a generally vertical section 1840 extending downwardly into sump 98 through the open top 98a thereof. The open end 184k of supply tube 184 is situated within sump 98 below the level of inlet port 130. In this manner, it will be appreciated that cryogenic liquid 20 from storage Dewar 12 will flow by gravity feed through supply line 38 and supply tube 184 into sump 98.

Again referring to FIG. 2, note that vent line 40 includes a section 400 which extends through back flange 108. Vent line section 400 is surrounded by a vacuum jacket manifold extension 186 which also extends through back flange 108. The end 186' of manifold extension 186 is interior of vacuum enclosure 96. The space 188 between vent line section 400 and vacuum jacket manifold extension 186 communicates with region 46, and so forms part of the vacuum space insulating vent line 40. Vent line 400 itself extends through mainfold end 186 and is connected via a coupling 190 to a vent tube 192.

As best shown in FIGS. 2 and 3, vent line 192 is generally horizontal, and terminates in a vertically extending vent dip tube 194 extending into sump 98 through the open end 98a thereof. The lower open end 196 of vent dip tube 194 preferably is situated above the level of inlet port 130. A blowby tube 198 is connected to piston ring blowby port 162 via an appropriate connector 200. The other end of blowby line 198 communicates with a Venturi 202 (within vent tube 192 opposite vent dip tube 194) via a connector 204. Venturi 202 has its open end pointing toward vent line connector 190, the open end being situated just downstream of vent dip tube 194. Just upstream of vent dip tube 194 is a flange portion 203 which completely closes communication around the exterior of Venturi tube 202 between blowby line 198 and vent tube 192.

As best shown in FIG. 2, a discharge tube 206 extends from discharge port 140 to back flange 108. Appropriate couplings 208 and 208' are used to connect discharge tube 206, via an opening through back flange 108, to discharge line 98. A lowpressure bleed tube 210 having an open end 212 communicates with bleed line 102 through back flange 108, tube 210 and line 102 being attached by means of appropriate connectors 214 and 214.

Dewar 96 (see FIGS. 2 and 3) has an outer wall 96a separated from an inner wall 96b by a vacuum space 216. Dewar 96 completely encloses sump 98, cold end 94, supply tube 184, vent tube 192, ring blowby line 198,

sealingly attached to said back flange to complete said said pump having a pumping element including a suction port discharge tube 206, and lowpressure bleed tube 210. Dewar and a discharge Port Said System Comprising:

96 is connected to back flange 108 by means of bolts 216. A springenergized Teflon seal 220 insures a pressuretight connection therebetween.

Although back flange 108 is not itself vacuum insulated, the number of penetrations therethrough making such vacuum insulation impractical, note that supply and vent lines 38 and 40 passing through back flange 108 are individually vacuum insulated. Moreover, discharge line 98 passes directly through flange 108. Thus, the discharge fluid in line 98 acts as a heat transfer medium, removing heat from back flange 108 and thereby keeping heat leakage from back flange 108 into the interior of Dewar enclosure 96 to a minimum.

In operation, cryogenic liquid from storage Dewar 12 flows by gravity feed into sump 98 via vacuum jacketed supply line sections 38a, 38 and 38c and via supply tube 184. Cryogenic liquid in sump 98 then floods input port 130 of pump 6, providing flooded suction to pumping element 94. By providing such flooded suction, the pump exhibits low net positive suction head.

Sump 98 is spaced from discharge port 140 to minimize heat leakage from the discharge line into the supply liquid. Further, the entire cold end, including sump 98, is vacuum insulated by Dewar enclosure 96, a long heat path thus being provided from ambient temperature to suction liquid at cryogenic temperature.

When valve 54 is open, the region within Dewar enclosure 96 is at the same pressure as the vapor space 22 within storage Dewar 12. As a result, when cryogenic liquid within suction sump 98 rises above the level of the open end 196 of vent dip tube 194, the excess liquid flows back to storage Dewar 12 via vent line 40.

As piston 92 reciprocates, cryogenic liquid from sump 98 is pumped to vaporizer 8 via discharge port 140, discharge tube 208 and discharge line 98. During the forward (discharge) stroke of piston 92, some of the fluid within chamber 124 passes around guide ring 128 and piston rings 126, and is forced out through ring blowby port 162 into blowby tube 198. This blowby fluid flows through Venturi 202, causing a suction in vent dip tube 194 which tends to aspirate sump 98. This Venturi action enhances the flow of excess cryogenic liquid from sump 98 back to storage Dewar 12. Alternatively expressed, the stream of twophase liquid in vent tube 198 and vent line 98 helps maintain adequate pressure differential between supply line 18 and vent line 40 to assist circulation of cryogenic liquid through the system. This in turn results in a short stay time for the liquid within sump 98.

While the invention has been described with respect to several physical embodiments constructed in accordance therewith, it will be apparent to those skilled in the art that various modifications and improvements may be made without departing from the scope and spirit of the invention.

I claim:

1, A vacuum insulated supply for a cryogenic pump, said pump having a pumping element including a suction port and a discharge port, said system comprising:

a Dewar enclosure surrounding said pumping element,

a sump within said enclosure and spaced from said discharge port, said suction port projecting into said sump, and

means for supplying cryogenic liquid into said sump, and

wherein said Dewar enclosure comprises:

a back flange rigidly attached to said pump, said pumping element projecting through said back flange, said back flange forming a wall of said enclosure, and

a generally cylindrical Dewar having a closed end and an open end, said Dewar covering said pumping element and said sump, the open end of Said Dewar being a Dewar enclosure surrounding said pumping element,

a sump within said enclosure and spaced from said discharge port, said suction port projecting into said pump, and

means for supplying cryogenic liquid into said sump, comprising;

a vent tube passing through a wall of said enclosure,

a vent dip tube extending into said sump and communicating with said vent tube, and

a supply tube entering through a wall of said enclosure and extending into said sump below the level of said vent dip tube.

3. A system according to claim 2 adapted for use with a conventional cryogenic liquid storage Dewar, said supply tube communicating with the liquid supply outlet of said storage Dewar, said vent tube communicating with the vent outlet of said storage Dewar.

4. A system according to claim 2 wherein said supply tube extends into said sump to a level below said suction port and wherein said vent dip tube extends into said sump to a level above said suction port.

5. A system according to claim 4 further comprising a Venturi tube within said vent tube adjacent said vent dip tube, and means for providing the ring blowby from said pump to said Venturi tube.

6. A system according to claim 5 wherein said pumping element includes a ring blowby port, and wherein said means for providing comprises a blowby tube connecting said ring blowby port and said Venturi tube.

7. In a cryogenic pump system including a storage Dewar containing a liquid atcryogenic temperatures, and a pump having a pumping element including a suction port and a discharge line, the imprcvement comprising:

interconnecting apparatus including vacuum insulated supply and vent lines leading from said storage Dewar,

a Dewar enclosure surrounding said pumping element,

a sump within said enclosure and spaced from said discharge line, said suction port projecting into said sump,

first and second vacuum jacket manifold extensions proj ecting through a wall of said enclosure, said supply and vent lines extending respectively through said first and second extensions,

a vent tube within said enclosure and communicating with said vent line,

a vent dip tube extending into said sump to a level above said suction port, said dip tube communicating with said vent tube, and

a supply tube within said enclosure and communicating with said supply line, said supply tube extending into said sump to a level below said suction port.

8. A vacuum insulated supply system for a cryogenic pump, said pump having a pumping element including a suction port and a discharge port and having a discharge tube extending from said discharge port, said system comprising:

a Dewar enclosure forming a first reservoir space, said pumping element and a portion of said discharge tube being situated within said first reservoir space,

a sump within said first reservoir space and forming a second reservoir, said suction port projecting into said second reservoir, and

means for supplying cryogenic liquid into said sump, said cryogenic liquid being confined to within said second reservoir to provide flooded suction to said suction port, said discharge port and said discharge tube portion being spaced from said sump and therefore out of contact with said supplied cryogenic liquid. 

1. A vacuum insulated supply system for a cryogenic pump, said pump having a pumping element including a suction port and a discharge port, said system comprising: a Dewar enclosure surrounding said pumping element, a sump within said enclosure and spaced from said discharge port, said suction port projecting into said sump, and means for supplying cryogenic liquid into said sump, and wherein said Dewar enclosure comprises: a back flange rigidly attached to said pump, said pumping element projecting through said back flange, said back flange forming a wall of said enclosure, and a generally cylindrical Dewar having a closed end and an open end, said Dewar covering said pumping element and said sump, the open end of said Dewar being sealingly attached to said back flange to complete said enclosure.
 2. A vacuum insulated supply system for a cryogenic pump, said pump having a pumping element including a suction port and a discharge port, said system comprising: a Dewar enclosure surrounding said pumping element, a sump within said enclosure and spaced from said discharge port, said suction port projecting into said sump, and means for supplying cryogenic liquid into said sump, comprising; a vent tube passing through a wall of said enclosure, a vent dip tube extending into said sump and communicating with said vent tube, and a supply tube entering through a wall of said enclosure and extending into said sump below the level of said vent dip tube.
 3. A system according to claim 2 adapted for use with a conventional cryogenic liquid storage Dewar, said supply tube communicating with the liquid supply outlet of said storage Dewar, said vent tube communicating with the vent outlet of said storage Dewar.
 4. A system according to claim 2 wherein said supply tube extends into said sump to a level below said suction port and wherein said vent dip tube extends into said sump to a level above said suctIon port.
 5. A system according to claim 4 further comprising a Venturi tube within said vent tube adjacent said vent dip tube, and means for providing the ring blowby from said pump to said Venturi tube.
 6. A system according to claim 5 wherein said pumping element includes a ring blowby port, and wherein said means for providing comprises a blowby tube connecting said ring blowby port and said Venturi tube.
 7. In a cryogenic pump system including a storage Dewar containing a liquid at cryogenic temperatures, and a pump having a pumping element including a suction port and a discharge line, the improvement comprising: interconnecting apparatus including vacuum insulated supply and vent lines leading from said storage Dewar, a Dewar enclosure surrounding said pumping element, a sump within said enclosure and spaced from said discharge line, said suction port projecting into said sump, first and second vacuum jacket manifold extensions projecting through a wall of said enclosure, said supply and vent lines extending respectively through said first and second extensions, a vent tube within said enclosure and communicating with said vent line, a vent dip tube extending into said sump to a level above said suction port, said dip tube communicating with said vent tube, and a supply tube within said enclosure and communicating with said supply line, said supply tube extending into said sump to a level below said suction port.
 8. A vacuum insulated supply system for a cryogenic pump, said pump having a pumping element including a suction port and a discharge port and having a discharge tube extending from said discharge port, said system comprising: a Dewar enclosure forming a first reservoir space, said pumping element and a portion of said discharge tube being situated within said first reservoir space, a sump within said first reservoir space and forming a second reservoir, said suction port projecting into said second reservoir, and means for supplying cryogenic liquid into said sump, said cryogenic liquid being confined to within said second reservoir to provide flooded suction to said suction port, said discharge port and said discharge tube portion being spaced from said sump and therefore out of contact with said supplied cryogenic liquid. 